{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 字典排序输出"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Python 3.7以前的版本中，字典本身是无序的，需要排序时，可以将字典的元素、键或值转为列表再排序输出。  \n",
    "3.7以后的版本字典顺序确保为插入顺序。  \n",
    "字典视图dict.keys()、dict.values()和dict.items()都是可逆的，同时可以作为排序函数sorted()的参数，排序返回结果为列表。  \n",
    "语法如下："
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "```python\n",
    "sorted(iterable, *, key=None, reverse=False)\n",
    "```"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### 字典名或dict.keys()为参数可返回键的排序列表"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "['Ana', 'Bob', 'Jack', 'Tom']\n",
      "['Ana', 'Bob', 'Jack', 'Tom']\n"
     ]
    }
   ],
   "source": [
    "info = {'Tom': 21, 'Bob': 18, 'Jack': 23, 'Ana': 20}\n",
    "sort_info = sorted(info)        # 直接对字典排序时，等价于对info.keys()排序 \n",
    "sort_key = sorted(info.keys())  # 对info.keys()排序 \n",
    "print(sort_key)    # ['Ana', 'Bob', 'Jack', 'Tom']\n",
    "print(sort_info)   # ['Ana', 'Bob', 'Jack', 'Tom']"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<img src=\"images/ch7/29.png\" style=\"zoom:80%;\">\n",
    "\n",
    "### dict.values()为参数可返回值的排序列表"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[18, 20, 21, 23]\n"
     ]
    }
   ],
   "source": [
    "info = {'Tom': 21, 'Bob': 18, 'Jack': 23, 'Ana': 20}\n",
    "sort_value = sorted(info.values())  # 对info.values()排序 \n",
    "print(sort_value)  # [18, 20, 21, 23]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<img src=\"images/ch7/30.png\" style=\"zoom:80%;\">\n",
    "\n",
    "### dict.items()为参数可对列表元素进行排序，默认根据键值排序"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "[('Ana', 20), ('Bob', 18), ('Jack', 23), ('Tom', 21)]\n",
      "<class 'list'>\n"
     ]
    }
   ],
   "source": [
    "info = {'Tom': 21, 'Bob': 18, 'Jack': 23, 'Ana': 20}\n",
    "sort_item = sorted(info.items())  # 对info.items()排序，默认根据键值排序 \n",
    "print(sort_item) \n",
    "print(type(sort_item))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<img src=\"images/ch7/31.png\" style=\"zoom:50%;\">"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "参数key是一个函数，用来选取参与比较的元素，可结合lambda表达式；  \n",
    "参数reverse则是用来指定排序是升序还是降序，reverse = True是降序，reverse = False是升序。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [],
   "source": [
    "info = {'Tom': 21, 'Bob': 18, 'Jack': 23, 'Ana': 20}\n",
    "sort_age = sorted(info.items(), key=lambda item: item[1], reverse = True)\n",
    "print(sort_age)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<img src=\"images/ch7/32.png\" style=\"zoom:80%;\">"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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